Monolithic base-metal glass-ceramic capacitor

Abstract

A monolithic ceramic capacitor has base-metal electrodes buried in a high dielectric constant reduction resistant glass-ceramic body. The glass component is an alkaline earth aluminoborate glass. The ceramic component is a barium titanate. The capacitor body is sintered at from 950° C to 1080° C in a low partial oxygen atmosphere. The buried electrode may be elementary copper.

What is claimed is: 
     
       1. A monolithic ceramic capacitor comprising: a reduction resistant glass-ceramic body having at room temperature a dielectric constant greater than 1000 and having a characteristic sintering and full densification temperature of from 1080° C to 950° C, said body consisting of from 5 to 15% by weight of a non-crystalline glass phase and from 85 to 95 percent by weight of a crystalline ceramic phase having a characteristic sintering and densification temperature greater than about 1200° C, said glass phase consisting essentially of an alkaline earth aluminoborate glass wherein said alkaline earth is selected from barium, strontium and calcium, said crystalline phase being an alkaline earth metal titanate wherein at least 50 mole percent of said alkaline earth metal is barium; a base metal electrode being buried within said reduction resistant glass-ceramic body; and another metal electrode contacting said body and being in capacitive relationship with said buried electrode. 
     
     
       2. The monolithic capacitor of claim 1 wherein said base metal is selected from copper, nickel, cobalt and alloys thereof. 
     
     
       3. The monolithic capacitor of claim 2 wherein said base metal consists essentially of copper. 
     
     
       4. The monolithic capacitor of claim 1 wherein said alkaline earth of said glass is partially replaced by magnesium. 
     
     
       5. The monolithic capacitor of claim 1 wherein an alkali-metal is substituted for up to 50 mole percent of said alkaline earth of said glass. 
     
     
       6. The monolithic capacitor of claim 1 wherein zirconium is substituted for up to 20 mole percent of the titanium of said titanate. 
     
     
       7. The monolithic capacitor of claim 1 wherein said titanate phase consists essentially of from 50 to 75 mole percent barium titanate and from 25 to 50 mole percent strontium titanate. 
     
     
       8. The monolithic capacitor of claim 1 wherein the said alkaline earth metal of said titanate is replaced by up to 8 mole percent calcium. 
     
     
       9. The monolithic capacitor of claim 1 wherein said alkaline earth metal titanate consists essentially of 60 mole percent barium titanate, 32.2 mole percent strontium titanate and 7.8 mole percent calcium titanate. 
     
     
       10. The monolithic capacitor of claim 1 wherein said glass phase includes no more than about 1 mole percent silica. 
     
     
       11. A method for making a monolithic ceramic capacitor having a reduction resistant glass-ceramic body exhibiting a dielectric constant at room temperature greater than 1000 and having a buried base metal electrode comprising: (a) preparing a slip consisting of a glass powder, a precursor powder of a crystalline ceramic material and a binder medium, said glass consisting essentially of an alkaline earth aluminoborate glass wherein said alkaline earth is selected from barium, strontium and calcium, said at least one ceramic material having a characteristic sintering and densification temperature greater than 1200° C, said ceramic material being a titanate of alkaline earth metal wherein at least 50 mole percent of said alkaline earth metal is barium, said glass powder being from 5-15% by weight of said glass and said ceramic powders combined;   (b) forming a plurality of layers of said slip;   
     
     
       (c) preparing an electroding base metal paste comprised of base metal particles and a binder medium and applying a coating of said paste to a surface of at least one of said layers; (d) stacking at least two of said layers so as to bury within said stack said electroding base metal coating of said at least one layer;   (e) heating said stack with said buried base metal coating at a temperature of from 1080° C to 950° C in an atmosphere of partial oxygen pressure less than 3×10 -6  atmospheres to sinter and fully densify said glass-ceramic stack, and to fire said buried coating to form a buried base metal electrode within said sintered capacitor body; and   (f) applying to said stack another metal coating in spaced relationship to said buried electrode to serve as a second electrode of said capacitor.   
     
     
       12. The method of claim 11 wherein, at the particular temperature of said heating, said partial oxygen pressure is less than that required for metal to metal-oxide thermodynamic equilibrium. 
     
     
       13. The method of claim 11 additionally comprising applying a film of said base metal paste to a face of said stack and in contact with an edge of said at least one electroding coating prior to said heating to provide an electrical termination to said buried electrode. 
     
     
       14. The method of claim 11 wherein said base metal is selected from copper, nickel, cobalt and alloys thereof. 
     
     
       15. The method of claim 11 wherein said base metal consists essentially of copper. 
     
     
       16. The method of claim 15 wherein said temperature of said heating is about 1050° C and said partial oxygen pressure is about 3×10 -6  atmospheres of oxygen. 
     
     
       17. The method of claim 11 wherein said alkaline earth of said glass is partially replaced by magnesium. 
     
     
       18. The method of claim 11 wherein an alkali metal is substituted for up to 50 mole percent of said alkaline earth of said glass. 
     
     
       19. The method of claim 11 wherein zirconium is substituted for up to 20 mole percent of the titanium of said titanate. 
     
     
       20. The method of claim 11 wherein said titanate consists essentially of from 50 to 75 mole percent barium titanate and from 25 to 50 mole percent strontium titanate. 
     
     
       21. The method of claim 11 wherein said alkaline earth metal titanate consists essentially of 60 mole percent barium titanate, 32.2 mole percent strontium titanate and 7.8 mole percent calcium titanate.